A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

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Part A

How many chromosomes do you expect to see in karyotypes of the parents?

 

Part B

What term best describes this kind of chromosome abnormality?

 

Part C

What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes?

asked Nov 23, 2012 in Genetics by GeneX ~Top Expert~ (7,947 points)
    

1 Answer

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Part A

One parent is expected to have 46 chromosomes and the other is expected to have 45 chromosomes.

 

Part B

A fusion of two acrocentric chromosomes (Robertsonian translocation).

 

Part C

1/3

answered Nov 23, 2012 by GeneX ~Top Expert~ (7,947 points)

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